4.3 mm holes, 20 mm deep

[Chaz]

Cool, if you look I think you can just buy 1 bit at a time for 99p all in or something from another seller, saves buying a box of 10.

I'll confirm what I've got if you want and send you?

Sure, thanks, happy to pay.

[cncmachineokk]

I have 4mm endmill length 22mm.

[Chaz]

I have 4mm endmill length 22mm.

Where did you get these from?

[Chaz]

So I tried to drill this today, 0.25mm pecks, 24K RPM, 75mm/min plunge. Went OK initially however about a third of the way and the drill snapped. I didnt want to go faster however it was just rubbing most of the time, was the feedrate too low? It had a mix of air and WD40 on it all the time.

Argh.

[johngoodrich]

what material are you drilling?

[Chaz]

what material are you drilling?

Alu.

[m_c]

For deep hole drilling, you really need good lubrication, and good chip clearance.

I've got an aluminium part that I drill on the lathe using a 6.8mm drill and 30mm deep (about 4.5 dia x depth). If the flood coolant fails (even just getting knocked away from hitting the drill), the drill will be welded to the part and snapped within a couple parts.
Polished drills greatly reduce chip welding (I use Phantom 11.160's, which are a polished cobalt stub drill).

For good chip clearance, you really need to ensure you're getting a good chip by using a reasonable DOC, which you may struggle to do with your spindle.

Having just ran the figures based on the drills I use, the optimum speed in soft aluminium is around 4400RPM, with a DOC of 0.135 per revolution, which should result in a required spindle torque of 0.7NM for a sharp drill.
Even with a solid carbide drill, the max speed is 12500rpm, but with a slightly higher DOC (and subsequently higher torque requirement - I've only got my spreadsheet setup for 11.160 drills)

The key thing is DOC and torque. Your spindle should be pretty much constant torque regardless of speed, so if it can't manage the require torque at a few thousand RPM, then it's not likely to manage at a higher speed. You could set the VFD to give a torque boost at lower RPM (increase the max current), but you do risk overheating the windings, however for peck drilling the load will be intermittent.

[Chaz]

For deep hole drilling, you really need good lubrication, and good chip clearance.

I've got an aluminium part that I drill on the lathe using a 6.8mm drill and 30mm deep (about 4.5 dia x depth). If the flood coolant fails (even just getting knocked away from hitting the drill), the drill will be welded to the part and snapped within a couple parts.
Polished drills greatly reduce chip welding (I use Phantom 11.160's, which are a polished cobalt stub drill).

For good chip clearance, you really need to ensure you're getting a good chip by using a reasonable DOC, which you may struggle to do with your spindle.

Having just ran the figures based on the drills I use, the optimum speed in soft aluminium is around 4400RPM, with a DOC of 0.135 per revolution, which should result in a required spindle torque of 0.7NM for a sharp drill.
Even with a solid carbide drill, the max speed is 12500rpm, but with a slightly higher DOC (and subsequently higher torque requirement - I've only got my spreadsheet setup for 11.160 drills)

The key thing is DOC and torque. Your spindle should be pretty much constant torque regardless of speed, so if it can't manage the require torque at a few thousand RPM, then it's not likely to manage at a higher speed. You could set the VFD to give a torque boost at lower RPM (increase the max current), but you do risk overheating the windings, however for peck drilling the load will be intermittent.

Thanks.

Thing is, these high speed spindles dont even turn below 150 rpm and at low speed are very easy to stall. Possibly the same at higher RPM however the momentum probably keeps it going.

Ive heard of bumping up the current, do you know where on the Chinese Hyaungyang VFD this is done?

What feedrate would you use at 12500 rpm with those drills? I did speak to them however being charged an admin fee and postage, higher than the cost of the bits put me off. Perhaps I need to look at this again.